Let us uplift facebar8/13/2023 That way, my cumulative brace force never gets excessively large.Best friends hold a special place in our hearts, and when your friend becomes more like a brother or sister to you, that is a priceless gift. In the case of a long roof with only joists, say with tilt-up walls, then I X-brace between the joists every 5 or 6 joists. So my uplift bracing is only carried over 4-6 joists at at time, typically. When I frame out a building, I like to use W-beams at the columns, and joists in between. The way I do it works well in most cases, where you don't have too many joists in a row. I don't know if this is really true behavior, but also don't want to take a chance. So does each joist then "apply" a buckling load to the one brace, or does only one buckling load exist? Well, if you think that only one load exists, then the continuous brace from joist to joist would then be a zero force member, if all the buckling load was taken out only at the last joist. Well, if you brace one joist, it won't buckle, but the others still want to. Now the entire group of joists could buckle together in the same direction. Let's say you connected the bottom chord of several joists together, but did not tie it off at the end. Personally, I think it should be additive in some way. RE: Uplift Bridging minorchord2000 (Structural) 30 Dec 08 11:49Ĭlansman: there is definitely debate in articles I have read, and people I talked to, regarding additive nature of bracing requirement. This can result in additional deck fastening in the area of the brace. And you should consider the normal deck stresses (uplift, diaphragm shear) due to the wind event at the same time as your uplift brace load. So now you have to ensure your deck can take the point load, or figure out how to distribute it over a large enough area. Typically you would bring it back up to the deck diaphragm. The last thing you need to worry about is how you resist the brace force at the end of the brace. So you can see, that it is not much of an increase in this case. But if I run a continuous angle all the way across, with x-bracing at each end, the maximum force would be 8/2*1.5k, or 6 kip. So now if I only design a single brace from teh bottom chord up to the next adjacent top chord (L~6'), it would need to be L2x2x3/16. So my compression flange force is 75 kip. So lets say I have 8 W16 beams, spaced 5 feet apart, with a moment of 100 k-ft in each. Just to make sure I am convered, I add the forces up and design the angle for the total sum. If you do it this way, there is some debate as to whether the 2% at each beam is cumulative in the brace. Then at the end (or also sometimes at some intermediate point), I X-brace the last bay, to bring the load up to the deck. If I have many beams side by side, like you say you have, I run a continuous angle across the bottoms of each. Design a single angle for that compression (and tension) force over the span length of the angle. In fact, testing has shown that even 1% is adequate for uplift bracing.īasically, find your maximum moment in the roof beam, calculate out the compression force in the compression flange, then take 2% of the force. The 2% rule is generally considered conservative.
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